The wavelength of a wave is the distance from one crest to the next. Click on image for full size (106K GIF) Windows to the Universe original artwork.

The wavelength of a wave describes how long the wave is. The distance from one crest to the next, or from one trough to the next, of a wave is its wavelength. Water waves in the ocean, sound waves in air, and light waves of electromagnetic radiation all have wavelengths.

The greek letter "l" (lambda) is often used in equations to represent wavelength. The wavelength of a wave is inversely proportional to the wave's frequency. A long wavelength means a low frequency, while a short wavelength means a high frequency.

Sound waves in the range that humans can hear have wavelengths ranging from less than 2 cm (an inch) to about 17 meters (56 feet). The waves of electromagnetic radiation that make up the visible light that we can see have wavelengths between 400 (purple light) and 700 (red light) nanometers (10^-9 meters).

The frequency and wavelength of a wave are related to each other by this equation:

l = c / f

where "l" is the wavelength, "c" is the speed of the wave, and "f" is the frequency. For light or other electromagnetic waves traveling in a vacuum, c = 299,792.458 km/sec (186,282 miles/sec), the speed of light. For sound waves moving through air, c is around 343 meters/second (767 miles/hour).

Red light with a frequency around 440 terahertz has waves about 682 nm long ( l = c / f = 2.99 x 10⁸ m s^-1 / 440 x 10¹² s^-1 = 682 x 10^-9 m = 682 nm).

Sound waves with a pitch of 1,000 hertz (1 kHz) produce waves with wavelengths around 34 cm (l = c / f = 343 m s^-1 / 1000 s^-1 = 0.343 meter).

The wavelength of a wave is the distance from one crest to the next. Click on image for full size (106K GIF) Windows to the Universe original artwork.

There are many kinds of waves all around us. Everyone knows about waves of water in the ocean. Did you also know that sound travels through the air in waves? Or that light is actually made up of waves of electromagnetic energy?

The length of a wave is called, well, its "wavelength". If you think about a wave in the ocean, its wavelength is the distance from the top of one wave (called the wave's "crest") to the top of the next wave. You can also measure the distance from the lowest point between two waves (called the wave's "trough") to the next trough. You should get the same distance either way.

The wavelengths of ocean waves we see at the beach are usually 10 or so meters (33 feet) or longer. Sound waves that humans can hear have wavelengths between about 2 cm (an inch) and 17 meters (56 feet). Waves of electromagnetic radiation that we see as light have really, really short wavelengths between 400 and 700 nanometers (a nanometer is one billionth of a meter!).

A wave also has a "frequency". The frequency is how often a crest goes by. The frequency of a wave depends on how fast the wave is moving. It also depends on the wavelength of the wave. Imagine two sets of waves that have the same speed. If one set has a longer wavelength, it will have a lower frequency (more time between waves). If the other set has a shorter wavelength, it will have a higher frequency (less time between waves). Wavelength and frequency go opposite of each other. Shorter wavelengths mean higher frequencies, while longer wavelengths mean lower frequencies.

Sound waves with a wavelength around 34 cm (about a foot) have a frequency of 1,000 hertz. A hertz is one wave per second. So a thousand sound waves can enter your ear in a second! Sound waves travel much faster than normal water waves. Sound waves move through the air at around 343 meters/second (767 miles/hour).

Light moves even faster AND has shorter wavelengths. These combine to give light extremely high frequencies. Red light has a wavelength of about 682 nanometers. Its frequency is around 440 terahertz. That's 440,000,000,000,000 hertz. That's a whole lot of waves going by in a second!

The wavelength of a wave is the distance from one crest to the next. Click on image for full size (106K GIF) Windows to the Universe original artwork.

Have you ever seen waves in the ocean or on a lake? If you watch the waves, you will see that they come one after another after another. Each wave is about as far away from the one in front of it as it is from the one behind it.

We can measure how far it is between the waves. Usually we measure from the top of one wave to the top of the next. The distance we measure is called the wavelength of the wave. The waves we see at a beach usually have a wavelength of 10 meters (33 feet) or longer.

Did you know that sound moves through the air in waves? Sound waves that people can hear have wavelengths between about 2 cm (an inch) and 17 meters (56 feet).

Light is also a kind of wave. Waves of electricity and magnetic force move through space. Those waves are called electromagnetic waves. Light is one kind of electromagnetic wave. Light waves are very, very, very short. Light waves have wavelengths between 400 and 700 nanometers (a nanometer is one billionth of a meter!).